Magnesium-manganese alloy for use in a pyrotechnical composition



material.

United States Patent 3,193,375 MAGNESHJM-MANGANESE ALLOY FOR USE IN A PYROTECHNICAL COWOSITION Walter Gtto August Marx, deceased, late of Haliein, Austria, by Annemarie Gertrude Marx, nee Wiemer, Hallein, Austria, Gerda Liseiotte Kemme, nee Marx, Henstedt-Rhen, near Kaltenkirchen, Germany, Ursula Maria Marx, Hallein, Austria, Hans Dieter Marx, Hallein, Austria, and Dorothea Friederike Marx, Hallein, Austria, heirs, and Stefan Gustav Marx, minor child, by Erich Angelberger, Hallein, Austria, trustee, and Rene Chave'e, Genk, Belgium, assignors to Knapsack-Griesheim Aktiengesellschaft, Knapsack,

near Cologne, Germany, a corporation of Germany No Drawing. Filed Sept. 5, 1962, Ser. No. 221,627 Claims priority, applicatigg 7Cerinany, Sept. 14, 1961,

The present invention relates to magnesium-manganese alloys suitable for use as pyrotechnical compositions.

It is known that magnesium, in spite of its great affinity for oxygen at room temperature, is relatively stable even during storage in the open air, because magnesium covers rapidly with a thin oxide skin which avoids further corrosion. The formation of such oxide skin has the result that magnesium in powder form, due to its then large surface, contains substantially more oxide than compact Still further, the presence of atmospheric moisture favors the oxide formation which considerably reduces the reactivity of magnesium in powder form after prolonged storage.

It is also known that pure magnesium in powder or granular form can be used for pyrotechnical purposes. Due to the aforesaid'great affinity of metallic magnesium, such magnesium powders when used in admixture with oxygen carriers, for example nitrates or'perchlorates, otter rather limited possibilities for storage and transport. Various proposals have already been made with the aim to protect magnesium against the action especially of oxidizing chemical agents or the open air. It has also been attempted to cover magnesium in powder form with a protective layer, for example, of silicon wax or other greasy material. By such treatment the stability to storage of the powder is admittedly increased, but the reactivity of the material is thereby strongly reduced. Alloys of magnesium with small amounts of other metals, such as beryllium, calcium or zirconium, partially led to an improved although non-uniform storability. On the other hand, the use of alloyed magnesium powder as a burning light source, for example in signal systems, involves strong and undesired color displacements of the light, or difficulties in foundry. Since, however, magnesium in powder form when used for pyrotechnical purposes, if desired in admixture with other substances, such as oxygen carriers, shall produce light of a definite coloration, or such mixtures must be ignited within pro-determined periods of time, the methods hitherto used for stabilizing magnesium for that particular purpose were little appropriate.

The present invention provides a finely divided binary magnesium/manganese alloy containing manganese in a proportion within the range of about 0.1 to 3% by weight, preferably about 0.5 to 1.0% by weight, for use as a pyrotechnical composition, which unexpectedly avoids all the above disadvantages.

The terms finely divided or state of fine subdivision as used herein are intended to mean granular and pulverized material.

It is admittedly old to use binary magnesium/ manganese alloys containing up to about 3% by weight manganese for the most varied application purposes, for example for extrusion. It is also old that such magnesium/manganese "ice alloys are relatively resistant to corrosion produced by outdoor influences. No proposals have, however, been made to use such alloy in the state of fine subdivision for pyrotechnical purposes, where the alloy, besides having corrosion resistant properties, which had to be evidenced to exist particularly inasmuch as finely subdivided powder is concerned, must have at the same time the property of avoiding a color displacement of the light on burning the powder. Moreover, the use of such alloy powders in signal systems calls for the observation of fairly accurately limited burning periods, which in turn is the result of the unexpected and extremely great corrosion resistance even of the finely divided powder of such alloys as will be demonstrated in greater detail in the working examples below.

After comminution, the alloy should have a granular or finely pulverized structure containing at least 99% by weight metal. The grain size of the powders used according to this invention isless than 900 microns, preferably within the range of to 75011.. The individual granular or pulverulent particles should exhibit a fairly spherical surface structure.

The present invention is based substantially on the ob servation that magnesium/manganese alloys having the above fine grain size can be ignited and burned even after having been stored for a prolonged time without the light intensity, ignition volocity, period of burning or the luminescence of the irradiated light being aifccted by the composition, manufacture, storage, and transport of the powdery alloy.

The most varied conventional mechanical means may be used for comminuting corresponding alloys. However, it has proved particularly advantageous to prepare the magnesiurn/ manganese alloy powder suitable for use as a pyrotechnical composition by first subjecting the alloy mass to a mechanical pre-commin-ution by milling, planing or turning, and then continuing comminution, in order to impart a fairly spherical surface structure to the granular or pulverulent material, in a pin mill, bafi'le mill or yet mill. The material should be mechanically comminuted in the atmosphere of an inert gas, for example a hydrocarbon or a noble gas, such as argon. Such round-off of spherical particles can also be prepared by first spraying or atomizing with the aid of a nozzle the molten metal and subsequently cooling or chilling it in the atmosphere of an inert gas with the proviso that such spraying or atomization leads to particles having relatively narrow grain size limits, so that uneconomic further processes, such as screening and re-melting of particles having a grain size outside the desired range, can be dispensed with.

It is here repeated that it is old to prepare aluminum and pure magnesium in powder form by spraying a melt thereof, but this known process must be carried out at least as far as magnesium is concerned in the atmosphere of an inert gas, for example argon, in order to avoid selfignition of the magnesium. Experience has shown, however, that sprayed or atomized magnesium is obtained in too fine a state of subdivision to be suitable for pyrotechnical purposes. On the other hand, customary scraping belts cannot be used for the manufacture of finely divided magnesium/manganese alloy powders, the alloy being so hard that it would damage the belt. In other words, the preferred mode of comminution used in accordance with the present invention resides in first cutting the material and then passing it, for example, through a pin mill.

The following examples serve to illustrate the invention, but they are not intended to limit it thereto:

The examples are specifically intended to demonstrate that the finely divided magnesium/manganese alloys exhibit as compared with pure magnesium in powder form considerable corrosion resistance sufiicient for the use of these alloys as pyrotechnical compositions, the corrosion resistance of magnesium/manganese alloys as such being known in the art.

Example 1 The material tested was (a) pure magnesium in powder form (99.9%) having a grain size of 200 to 430 1 and (b) a magnesium/manganese powder containing 1% by weight manganese and having the same grain size. In order to expose approximately equal surfaces to the action of moist air, the bulk weights of the two samples were first determined and corresponding weighed portions of the two samples were then tested.

The two samples were exposed for three months at room temperatures to the action of moisture-saturated air. After that time, the samples were dried for 12 hours in vacuo and weighed. After drying, the pure magnesium contained 0.9% oxide after the three months period, the magnesium/manganese powder as little as 0.1%, the percent figures being expressed in percent by weight and being calculated on the total amount of powder.

Example 2 A further test was conducted over a period of 72 hours at 95 C. in steam-saturated air, the powders used having grain sizes corresponding to those used in Example 1. In each case, c. of the two powder samples were used. In the case of pure magnesium powder, Weighing before the test and after the drying after three days indicated a weight increase from 7.1215 g. to 7.1724 g., corresponding to 0.72%, while in the case of magnesium/manganese powder the weight increased from 7.9157 to 7.9362 g., corresponding to an increase in weight of 0.26%.

The above example shows clearly, that the magnesium/ manganese alloy possesses considerable advantages even in the state of fine subdivision over pure magnesium as regards resistance to corrosion. The alloy powder could be used for pyrotechnical purposes without the necessity of subjecting it to detrimental treatment, such as greasing the powder.

Example 3 To more distinctly dififerentiate between the two powders, the test conditions were varied by exposing the two powders to more severe heat-moisture stress. To this end, the two powders, which were in a sinter crucible, were introduced into a closed vessel, in which water was permanently kept boiling to produce steam. The two samples were thus exposed for 12 hours to the action of steam. After having been dried for 12 hours in vacuo, the samples were weighed and the increase in weight determined. The weight increase in the case of pure magnesium amounted to 2.63%, corresponding to a weight of 7.1470 g. before the test and a weight of 7.3362 g. after drying. The weight increase in the case of magnesium/manganese powder amounted to 0.30% corresponding to a weight of 7.7719 g. before the test and 7.7952 g. after drying.

Following the above test conducted under the action of steam, the pure magnesium powder had distinctly darkened as regards its outer appearance. Examination of all powders under the microscope indicated that after the above treatment and contrary to the same material before the test and contrary to the alloyed magnesium/manganese powder before and after the test, the grains of the pure magnesium powder alone exhibited a strongly splitted and fissured surface, which indicates strong corrosion.

We claim:

1. A method of producing a pyrotechnic efiiect comrpising mixing with a pyrotechnical composition a binary alloy in the form of finely divided particles consisting essentially of magnesium and 0.1 to 3 percent by weight of manganese, said finely divided particles having a grain size smaller than 900 microns.

2. The method of claim 1 wherein the manganese is present in from 0.5 to 1.0 percent by weight of the alloy.

3. The method of claim 1 wherein the particles consist of at least 99 percent by weight of metal.

4. The method of claim 1 wherein the particles have a grain size of between 50 and 750 microns.

5. The method of claim 1 wherein the particles have a spherical surface.

References Cited by the Examiner UNITED STATES PATENTS 1,351,865 9/20 Nicol .5 2,088,204 7/37 Hansgirg 75.5 2,353,612 7/44 Gardner 75--122 2,450,892 10/48 Hale 149- 37 2,885,277 5/59 Fitzpatrick 149-37 FOREIGN PATENTS 522,463 6/40 Great Britain.

OTHER REFERENCES Goetzel: Treatise on Powder Metallurgy, vol. II, Interscience Publishers, Inc., New York, 1950, page 739.

Goetzel: Treatise on Powder Metallurgy, vol. 1, 1949, pages 35-48.

DAVID L. RECK, Primary Examiner. 

1. A METHOD OF PRODUCING A PYROTECHNIC EFFECT COMRPISING MIXTURE WITH A PYROTECHNICAL COMPOSITION A BINARY ALLOY IN THE FORM OF FINELY DIVIDED PARTICLES CONSISTING ESSENTIALLY OF MAGNESIUM AND 0.1 TO 3 PERCENT BY WEIGHT OF MANGANESE, SAID FINELY DIVIDED PARTICLES HAVING A GRAIN SIZE SMALLER THAN 900 MICRONS. 